Axle Driving Apparatus

ABSTRACT

An axle driving apparatus for being mounted on the body frame of a vehicle and for independently rotating drive wheel members. The axle driving apparatus includes a first axle driving unit ( 18 L) leaving a housing ( 40 ) and a single axle ( 20 L), the single axle ( 20 L) defining a proximal end portion rotatably mounted in the housing ( 40 ) and a distal end portion extending outwardly from a first side of the housing ( 40 ). An enlarged region is defined by the housing ( 40 ), with the enlarged region extending substantially perpendicular to the longitudinal axis of the single axle ( 20 L). A hydraulic stepless speed change assembly ( 22 ) is disposed within the enlarged region. The speed change assembly ( 22 ) includes a hydraulic pump ( 52 ) having an input shaft ( 21 ) projecting from the enlarged region and includes a hydraulic motor ( 55 ) including an output shaft ( 74 ) drivingly connected to the single axle ( 20 L). The first axle driving unit ( 18 L) is used in conjunction with a second axle driving unit ( 18 R) which is adjacently disposed to the first axle driving unit ( 18 L) on the body frame of the vehicle and which is of substantially similar construction. However, the second axle driving unit ( 18 R) features a single axle ( 20 R) which extends outwardly from a second, opposite side of the housing ( 40 ) such that the axles ( 20 L,  20 R) are oppositely disposed.

TECHNICAL FIELD

This invention relates to an axle driving apparatus for independentlydriving the wheels of a self-propelled vehicle. In this particularinvention the axle driving apparatus includes axle driving unitsprovided with hydraulic stepless transmissions which drive single axlesand which are adjacently disposed on a vehicle to independently rotatethe drive wheels of such vehicle.

BACKGROUND ART

Axle driving units incorporating hydraulic stepless transmissions havebeen used to drive the axles of self-propelled vehicles for many years.Generally such units include a hydraulic pump driven by an input shaftand a hydraulic motor having an output shaft drivingly connected througha differential to a pair of oppositely disposed axles. An example ofsuch a unit is disclosed in U.S. Pat. No. 4,914,907. However, certainself-propelled vehicles perform tasks which require tight turningcapabilities and conventional hydraulic transmissions which drive a pairof axles through a differential gear assembly are not particularlysuited for such purposes. Instead, vehicles have been provided withaxles which are independently driven by separate axle drive units suchthat turns are accomplished by rotating, drive wheels on opposite sidesof the vehicle at different speeds and/or in different directions.Further, certain such axle driving units for independently drivingsingle axle have incorporated hydraulic transmissions. However, suchaxle driving units have required housings which are of substantialheight and substantial width in order to accommodate the hydraulic pumpand motor and the other necessary components. Accordingly, vehicles haverequired large body frames in order to accommodate two such axle drivingunits in a side-by-side disposition, thus ruling out use of the units onmany small vehicles. Further, even where a large body frame is provided,the center of gravity of the vehicle tends to be higher than isdesirable for good roadability due to the height of the axle drivingunits and the need to dispose the prime mover of the vehicle in anelevated position to efficiently drive the units. For example, in U.S.Pat. No. 5,127,215 a dual hydrostatic drive walk-behind mower isdisclosed, but it can be readily seen that the axle driving units ofthis mower require substantial vertical and lateral space such that alarge body frame is required. It will also be noted that due to theheight of the transmission housings, the engine must be disposed in anelevated position which results in the vehicle having an undesirablyhigh center of gravity. Moreover, multiple driving belts are required todrive the input shafts of the axle driving units. (See also, U.S. Pat.Nos. 4,809,796 and 5,078,222). In U.S. Pat. No. 4,819,508, atransmission system for working vehicles is disclosed which partiallysolves the problem of an undesirable center of gravity by reorientingthe engine such that the crank shaft is horizontally disposed. However,the axle driving mechanism still occupies substantial vertical space onthe body frame, making the center of gravity undesirably high. Further,reorientation of the engine complicates the drive belt systems fordriving both the axle driving units and the mower blades.

Therefore, it is an object of the present invention to provide an axledriving apparatus for independently driving axles on opposite sides of avehicle.

It is another object of the present invention to provide an axle drivingapparatus which includes side-by-side axle drive units incorporatinghydraulic transmissions which require limited vertical or lateral spacesuch that the axle driving apparatus can be used by small self-propelledvehicles, and such that vehicles utilizing such axle driving apparatusdefine low centers of gravity for improved roadability.

Yet another object of the present invention is to provide an axledriving apparatus having input shafts and a drive belt system whichfacilitates drivingly connecting the apparatus to the prime mover of thevehicle.

Still another object of the present invention is to provide an axledriving apparatus which is inexpensive to manufacture and maintain.

SUMMARY OF THE INVENTION

The present invention provides an axle driving apparatus forindependently driving a pair of drive wheels on a self-propelledvehicle. The apparatus of the present invention includes axle drivingunits which drive a single axle, and which are selectively configured asleft or right side axle driving units such that a pair of such units canbe adjacently disposed in a side-by-side orientation oil the body frameof the vehicle to drivingly support oppositely disposed drive wheels.Each of the axle driving units includes a housing comprising an upperhalf housing and a lower half housing joined to each other through aperipheral joint or junction surface. The left axle driving unitincludes a single axle which projects from the left side of the housingfor supporting a drive wheel on the left side of the vehicle. The rightdriving unit includes a single axle which projects from the right sideof its housing for supporting a drive wheel on the right side of thevehicle. Whereas the axles project from opposite sides in the left andright axle driving units, in the preferred embodiment the housing isprovided with bearing supports to accommodate the mounting of either aleft side projecting axle or a right side projecting axle. Accordingly,the housing can be alternatively used in the construction of a left sideaxle driving unit or a right side axle driving unit.

In each of the axle driving units, the housing defines an enlargedregion which extends perpendicular to the longitudinal axis of theoperatively associated axle such that the length of the housing isgreater than its width, thereby facilitating the side-by-side mountingof two axle driving units. This enlarged region accommodates themounting of a hydraulic stepless transmission which communicates thedriving force of the prime mover, or engine, of the vehicle on which theapparatus is mounted to the operatively associated axle. Thetransmission includes a center section which defines a pump mountingsurface on which a hydraulic pump is mounted and defines a motormounting surface on which a hydraulic motor is mounted. The centersection establishes closed circuit fluid communication between thehydraulic pump and motor and is configured to advantageously dispose thepump and motor in positions displaced from the single axle such thatboth the height and the width of the axle driving unit is reduced.Accordingly, the axle driving units call be mounted in a lower positionon the vehicle to produce a lower center of gravity aid can beaccommodated in a relatively narrow body frame.

The hydraulic pump includes an input shaft which projects from thehousing and which is drivingly connected by a driving belt to the primemover of the vehicle. The hydraulic motor includes an input or motorshaft drivingly connected with the operatively associated single axle.The input shaft of each of the adjacent axle driving units carries aninput pulley and a single driving belt is received around the inputpulleys and a drive pulley mounted on the crank shaft of the prime moverto effect rotation of the input shafts. Further, the reduced height ofthe axle driving units permits the input pulleys and the drive pulley tobe oriented in a triangular disposition and to be aligned on a common,substantially horizontal plane. Further, it allows the prime mover to bemounted in a low position on the body frame such that the vehicledefines a low center of gravity.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned features of the invention will be more clearlyunderstood from the Following detailed description of the invention readtogether with the drawings in which:

FIG. 1 illustrates a perspective view of a walk behind mower, such mowerbeing an example of one type of vehicle on which the axle drivingapparatus of the present invention can be used.

FIG. 2 illustrates a plan view, partially in section, of a walk behindmower having an axle driving apparatus of the present invention mountedthereon.

FIG. 3 illustrates a perspective view of an axle driving apparatus ofthe present invention.

FIG. 4 illustrates a plan view of an axle driving apparatus of thepresent invention.

FIG. 5 illustrates a plan view, partially in section, of an axle drivingunit of the present invention.

FIG. 6 illustrates a front elevation view, in section taken at A-A inFIG, 5, of an axle driving unit of the present invention.

FIG. 7 illustrates a rear elevation view, in section at B-B in FIG. 5,of an axle driving unit of the present invention.

FIG. 8 illustrates a rear elevation view, in section at C-C in FIG. 5,of an axle driving unit of the present invention.

FIG. 9 illustrates a side elevation view, in section at D-D in FIG. 5,of an axle driving unit of the present invention.

FIG. 10 illustrates a perspective view of a center section of an axledriving unit of the present invention.

FIG. 11 illustrates a plan view, partially in section, of an axledriving unit of the present invention,

FIG. 12 illustrates a rear elevation view, in section at C′-C′ in FIG.11, of an axle driving unit of the present invention.

FIG. 13 illustrates a plan view, partially in section, of an axledriving unit of a second embodiment of the present invention.

FIG. 14 illustrates a front elevation view, in section at E-E in FIG.13, of an axle driving unit of the second embodiment of the presentinvention.

FIG. 15 illustrates a rear elevation view, in section at F-F in FIG. 13,of an axle driving unlit of the second embodiment of the presentinvention.

FIG. 16 illustrates a side elevation view, in section at G-G in FIG. 13,of an axle driving unit of the second embodiment of the presentinvention.

FIG. 17 illustrates a perspective view of a center section of the secondembodiment of the present invention.

FIG. 18 illustrates a plan view, partially in section, of an axledriving unit of a third embodiment of the present invention.

FIG. 19 illustrates a front elevation view, in section at H-H in FIG.18, of an axle driving unit of the third embodiment of the presentinvention.

FIG. 20 illustrates a perspective view of a center section of the thirdembodiment of the present invention.

FIG. 21 illustrates a side elevation view, in section, of an axledriving unit of a fourth embodiment of the present invention.

FIG. 22 illustrates a plan view, partially in section, taken at I-I inFIG. 21, of an axle driving unit of the fourth embodiment of the presentinvention.

FIG. 23 illustrates a rear elevation view, in section taken at J-J inFIG. 22, of an axle driving unit of the fourth embodiment of the presentinvention.

FIG. 24 illustrates a side elevation view, in section, of an axledriving unit of a fifth embodiment of the present invention.

FIG. 25 illustrates a rear elevation view, in section taken at K-K inFIG. 24, of an axle driving unit of the fifth embodiment of the presentinvention,

FIG. 26 illustrates a perspective view of the center section of thefifth embodiment of the present invention.

FIG. 27 illustrates a plan view, partially in section, of an axledriving apparatus of the fifth embodiment of the present invention.

FIG. 28 illustrates a side elevation view, in section taken at L-L ofFIG. 27, of an axle driving apparatus of the fifth embodiment of thepresent invention.

FIG. 29 illustrates a rear elevation view, in section taken at M-M ofFIG. 24, of an axle driving apparatus of the fifth embodiment of thepresent invention.

FIG. 30 illustrates a rear elevation view, in section, of an axledriving unit of a sixth embodiment of the present invention.

FIG. 31 illustrates a plan view, partially in section, of an axledriving apparatus of the sixth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The axle driving apparatus of the present invention is designed forindependently driving a pair of drive wheels on self-propelled vehiclessuch as walk behind mowers, snow blowers, floor cleaning machines,riding lawn mowers, zero turn radius vehicles, and the like.Accordingly, although the axle driving apparatus is discussed below withrespect driving the drive wheels of a self-propelled walk behind mower,it will be understood that such apparatus can be used with variousvehicles.

In FIGS. 1 and 2, a walk behind mower utilizing an axle drivingapparatus of the present invention is illustrated generally at 10. Themower 10 includes a body frame 11 movably supported by oppositelydisposed drive wheels 12L and 12R. Secured to the forward portion of thebody frame 11 is a mower deck 13 which is supported by a pair of casterwheels 15L and 15R, and on which are rotatably mounted a plurality ofblade members 14 which are utilized for cutting grass and othervegetation.

The drive wheels 12L and 12R are rotatably driven by a prime mover, suchas the illustrated engine 16, mounted on the body frame It. Morespecifically, and as best illustrated in FIGS. 2-4, the axle drivingapparatus 10 includes adjacently disposed left and right axle drivingunits 18L and 18R, respectively, which are suspended from mountingmembers 19L, 19R, and 19C provided on the body frame 11. The axledriving units 18L and 18R support and selectively rotate the axles 20Land 20R oil which the drive wheels 12L and 12R are carried. In thisregard, each of the axle driving units 18L and 18R includes a speedchange mechanism which is drivingly connected to the operativelyassociated axle 20L or 20R such that the rotational speed and directionof the drive wheels can be independently selected. As will be discussedin detail below, in the preferred embodiment the speed change mechanismscomprise hydraulic stepless speed change transmissions 22 (e.g. FIG. 5).Further, each of the units 18L and 18R includes an input shaft 21, therotation of which operatively drives the hydraulic transmission 22. Inthe preferred embodiment, the input shafts 21 extend substantiallyvertically from enlarged portions of the housings of the axle drivingunits 18L and 18R. This vertical orientation is useful when the engineof the self-propelled vehicle has a vertically disposed crank shalt, asin the case of the illustrated mower 10. Given the relative dispositionof the input shafts 21 and the crank shaft 24 of the engine 16, theshafts 21 can be drivingly connected to the crank shaft 24 by as singledrive belt 25.

In the preferred illustrated embodiment, the crank shaft 24 is providedwith a drive pulley 26 about which the drive belt 25 is received, andeach of the shafts 21 is provided with an input pulley 28 around whichthe drive belt 25 is received. Further, the belt is routed between apair of tension pulleys 29 which are supported on the body frame 11.Preferably, the drive pulley 26 and the input pulleys 28 aretriangularly disposed in a common, substantially horizontal plane so asto make efficient use of the space within the body frame 11. It willalso be noted in this regard that the advantageous positioning ofcomponents within the axle driving units 18L and 18R, which will bediscussed in detail below, allows the housings of the axle driving unitsto be reduced in height compared with conventional axle driving units.This reduction in height, together with the vertical disposition of theinput shafts 21 and advantageous disposition of drive and input pulleys,allows the body frame 11, and the engine 16 mounted therein, to bereduced in height and disposed in a lower position, thereby lowering thecenter of gravity of the mower 10 and improving roadability.

As illustrated in FIG. 2, the engine 16 also serves to rotatably drivethe blade members 14. In this regard, each of the blade members 14 ismounted on a shaft 30 provided with a pulley 31. A drive belt 32 isreceived around a further drive pulley 34 mounted on the crank shaft 24and around the pulleys 31 to effect rotation of the blade members 14.Further, tensioning pulleys 35 are provided to maintain tension on thebelt 32 during operation.

It will be recognized by those skilled in the art that the operator ofthe mower 10 walks behind the mower during operation, and a steering bar36 is provided to facilitate the steering of the mower 10 during use.The mower 10 is moved in forward and reverse directions by rotating thedrive wheels 12L and 12R at the same speed, and turns are accomplishedby selectively rotating the drive wheels 12L and 12R at differentspeeds. As will become clear from the discussion below, the hydraulictransmissions 22 of the axle driving units 18L and 18R allow the speedand rotational direction of the drive wheels 12L and 12R to beindependently altered such that both the speed and the direction ofmovement of the mower can be controlled. Accordingly, steering controllevers 38L and 38R are mounted on the steering bar 36 and connected bysuitable linkages to transmission control levers 65 (discussed below) onthe axle driving units 18L and 18R. Further, an accelerator 39 ismounted on the steering bar 36 to control the operation of the engine16.

More specifically with respect to the axle driving apparatus of thepresent invention, FIGS. 2-12 illustrate the construction of onepreferred embodiment of the apparatus. As noted above, the apparatus ofthe present invention includes a pair of axle driving units 18L and 18Rwhich are adjacently disposed, and it will be noted that in thepreferred embodiment the units 18L and 18R are substantially identicalexcept for the disposition of the operatively associated axles 20L and20R. Accordingly, in discussing the Figures, components and featureswhich are common to both axle driving units will be referenced withcommon reference numerals.

The axle driving unit 18L includes a housing 40 comprising an upper halfhousing 40U and a lower half housing 40L joined to each other through aperipheral joint or junction surface. When the housing 40 is mounted inan operating position on the body frame 11 of the mower 10, the joistsurface is substantially horizontally disposed. As noted above, in thepreferred embodiment of the present invention, the speed changemechanism comprises a hydraulic stepless speed change transmission 22.Accordingly, the housing 40 is sealed such that lubricating oil can becharged into the housing and used as operating oil for the hydraulictransmission. It will also be noted that, in order to facilitate themounting of the unit 18L on the body frame 11, the housing 40 defines afirst mounting boss 41A at a forward left portion of the housing 40which releasably engages the left mounting member 19L of the body frame11. The housing 40 further defines a second mounting boss 41B at aforward right portion of the housing 40 which releasably engages thecenter mounting member 19C.

The axle 20L of the axle driving unit 18L projects from the left side ofthe housing, and driving wheel 12L mounts at the distal end of the leftaxle 20L. In order to rotatably support the axle 20L in the housing 40,the axle driving unit 18L includes a first bearing support 42 includinga hollow tube portion 43 defining a bearing seat for receiving a firstroller bearing 44. As best illustrated in FIG. 5, the first rollerbearing 44 rotatably supports the axle 20L proximate the point at whichthe axle projects from the housing 40. In the illustrated embodiment,the first bearing support 42 is provided in the upper half housing 40Usuch that the rotational axis of the axle 20L is positioned in ahorizontal plane disposed roughly midway along the vertical dimension ofthe housing 40 This disposition of the axle 20L results in a wellbalanced axle driving unit and, as illustrated in FIG. 9, allows thefinal gear 94 (discussed below) to be accommodated in the housingwithout providing an expanded region in the lower half housing whichwould reduce ground clearance. However, it is contemplated that theroller bearing support 42 can be cooperatively defined by the upper andlower half housings 40U and 40L where the joint surface between theupper and lower housings is alternatively disposed in a common planewith the rotational axis of the axle 20L, or can be provided in thelower half housing 40L, where the join surface is disposed in a planeabove the rotational axis of the axle 20L.

A second bearing support 45 is also provided which defines a bearingseat for receiving a second roller bearing 46. As illustrated, thesecond roller bearing supports the proximal end of the axle 20L In thepreferred embodiment, the second bearing support 45 comprises a firstcomponent 45A provided on the upper half housing 40U, and a secondcomponent 45B provided on the lower half housing 40L such that thecomponents 45A and 45B cooperatively define the bearing seat forreceiving the second roller bearing 46 (See FIG. 8).

In order to accommodate the transmission 22, the real portions (portionstoward the rear of the mower 10) of upper and lower half housings 40Uand 40L are enlarged in a direction perpendicular to the longitudinalaxis of the axle 20L. Therefore, the housing of the axle driving unit islonger (length L) than it is wide (width W; see FIG. 5) whichfacilitates the side-by-side mounting of the two axle driving units. Thehydraulic stepless transmission 22 includes a center section 48 which ismounted in the enlarged region of the housing 40. As shown in FIG. 10,the center section 48 is a single, elongated piece having an uppersurface 49 and a side surface 50 which are adjacent and perpendicular toeach other. A pump mounting surface 51 is defined at the rear portion(toward the rear of the mower 10) of upper surface 49 for mountingthereon a hydraulic pump 52. At the forward portion of side surface 50,a motor mounting surface 54 is defined for mounting a hydraulic motor55. As shown in FIG. 9, the center of the motor mounting surface 54extends in parallel to pump mounting surface 51 and is offset downwardlytherefrom by a height H1. It will be recognized that by limiting thisoffset distance, the overall height of the enlarged region of thehousing 40 can be limited. Further, the pump mounting surface 51 of thecenter section 48 extends horizontally with respect to the axle 20L, andis rearwardly spaced from the axles which also facilitates the reductionof height of the housing 40.

As shown in FIG. 10, housing mounting faces 56 are formed on the uppersurface 49 of the center section 48 and are preferably disposed incommon plane with the pump mounting surface 51. Therefore, housingmounting faces 56 can be ground when the pulp mounting surface 51 isground so that the processing time for the center section 48 can bereduced. Bolt insertion bores are provided at the housing mounting faces56, and center section 48 is fixed to the inner wall of the enlargedregion of upper half housing 40U by connecting bolts inserted into thebores. Alternatively, the pump mounting surface 51 and the motormounting surface 54 can be provided integral to the inner wall of thelower half lousing 40L by increasing the thickness of such inner wall inthe enlarged region. However, it is preferable to use a center section48 which is separate from the housing to facilitate processing of thehousing, and to prevent oil from leaking out of the housing.

As illustrated in FIG. 6, a valve plate 58 is mounted onto pump mountingface 51 to accommodate the mounting of the hydraulic pump 52 of thehydraulic stepless transmission 22. In the preferred illustratedembodiment, the pump 52 comprises an axial piston type variabledisplacement hydraulic pump. In this regard, the hydraulic pump 52includes a cylinder block 59 rotatably disposed on the valve plate 58.Pistons 60 are fitted into a plurality of cylinder bores of cylinderblock 59 for reciprocating movement in response to biasing springs. Itwill be recognized by those skilled in the art that rotation of theinput shaft 21 serves to drive the hydraulic pump 52. In this regard,the input shaft 21 engages with a spline bore provided on the rotationalaxis of cylinder block 59 such that the cylinder block 59 rotates withthe input shaft 21. The input shaft 21 is rotatably supported at itsupper end portion by upper half housing 40U and a distal end portion 21Aof the shaft 21 extends out of the housing 40. The lower end portion 21Bof the input shaft 21 is received through a bore 61 provided in thecenter section 48 so as to be maintained in the proper axial alignment.One of the input pulleys 28 is secured to the upper end portion 21A ofthe input shaft 21 and, as note above, the pulley 28 is selectivelyrotated by the drive belt 25. It will also be noted that a cooling fan63 is mounted on the input shaft 21 for cooling the axle drive unitduring operation.

In the preferred illustrated embodiment, a trunnion-type movable swashplate 62 is provided for selectively varying the displacement of thehydraulic pump 52. In this regard, the swash plate 62 includes a firsttrunnion shaft 62A which is supported by a lid 64 mounted over allopening 67 in the upper half housing 40U, and includes a furthertrunnion shaft 62B which is supported by a bearing bore provided at theinner wall of upper half housing 40U (See FIG, 6). The trunnion shaft62A projects outwardly from the lid 64 and a speed control lever 65 ismounted on the projection. Accordingly, selected rotation of the controllever 65 pivots the swash plate 62 on the common rotational axis of thetrunnion shafts 62A and 62B. An opening is provided in the swash plate62 to accommodate the input shaft 21, and the swash plate 62 is movablydisposed such that the heads of the pistons 60 abut against a thrustbearing 66 of the swash plate 62. Accordingly, pivotal movement of theswash plate 62 alters the angular disposition of the thrust bearing 66as it engages the pistons 60, thereby allowing alteration of thedischarge direction and discharge rate of the hydraulic pump 52.

It will be understood that whereas an axial piston type variabledisplacement hydraulic pump is illustrated in the Figures and has beendescribed above, a radial piston type hydraulic pump or a gear type pumpmay be interchangeably used. Further, whereas in the embodiment of FIGS.2-12 the pump 52 incorporates a trunnion-type swash plate, it will beunderstood by those skilled in the art that a cradle-type swash platecan be interchangeably used.

In the preferred illustrated embodiment, the hydraulic motor 55comprises all axial-piston type fixed displacement hydraulic motor. Asbest illustrated in FIGS. 5 and 7, a valve plate 68 is mounted on themotor mounting surface 54 of the center section 48, and the hydraulicmotor 55 includes a cylinder block 69 which is rotatably disposed on theplate 68. A plurality of pistons 70 are fitted for reciprocatingmovement into a plurality of cylinder bores defined in the cylinderblock 69. The heads of pistons 70 abut against a thrust bearing 71 of afixed swash plate 72 disposed between upper half housing 40U and lowerhalf housing 40L. An input or motor shaft 74 engages a spline boreprovided on the rotational axis of cylinder block 69 such that the motorshaft 74 rotates with the cylinder block 69.

The rotational axis of cylinder block 69 is preferably positioned in thesame plane as the joint surface of the upper and lower half housings tofacilitate the rotational mounting of the motor shaft 74. In thisregard, one end of motor shalt 24 is supported by a bearing 75 which issandwiched between the upper half housing 40U and the lower half housing40L, and the other end of the shaft 74 is received by, and supported in,a receptor 76 provided in the center section 48. It will be noted that,when the hydraulic pump and the hydraulic motor are disposed on thecenter section 48 described above, input shaft 21 and motor shaft 74 areperpendicular to each other, and the input shaft 21 is offset from themotor shaft 74 by a length L2 (see FIG. 9) in the direction apart fromthe axle 20L.

As shown in FIGS. 5, 9, and 10, a pair of kidney-shaped ports 78A and78B is open on pump mounting face 51 of the center section 48 to take inor discharge oil in cylinder block 59. Further, a pair of kidney-shapedports 79A and 7913 is open on motor mounting face 54 to take in ordischarge oil in cylinder block 69. It order to establish fluidcommunication between the port 78A and the port 79A, a first oil passage80A is provided in the center section 48, and in order to establishfluid communication between the port 78B and the port 79B, a second oilpassage 80B is provided in the center section 48. Accordingly, a closedcircuit is defined to circulate the operating oil between the hydraulicpump and hydraulic motor. It will also be noted that a check valve meansis provided which includes a check valve (not shown) disposed in each ofthe passages 80A and 80B. The check valve means selectively places thepassages 80A and 80B in fluid communication with each other, therebyenabling the hydraulic motor to idle. A push rod 81 which projects fromthe upper half housing 40U is provided for manually actuating the checkvalves.

It will be recognized from the above that the hydraulic pump 52 andhydraulic motor 55, which are placed in closed circuit fluidcommunication by the advantageously configured center section 48,provide a hydraulic stepless speed change transmission. In this regard,the rotation of the input shaft 21 drives pump 52, and by selectivealtering the discharge direction and discharge rate of the pump 52through manipulation of the speed control lever 65, the hydraulic motorproduces stepless output rotation of the motor shaft 74.

In order to facilitate the operation of the transmission, operating oilsupply means is provided for replenishing oil that has leaked out fromthe center section 48. The supply means may be the hydraulic pumpitself, or, as in the preferred illustrated embodiment, a charge pump 82can be provided. The charge pump 82, as shown in FIG. 6, is a trochoidpump which is contained in a charge pump casing 84 biased toward acharge pump mounting surface 85 on the lower surface of center section48 by a spring member 83, with the spring member 83 being used foradjusting the discharge oil pressure of the charge pump 82. The chargepump 82 is driven by the input shaft 21 and is in fluid communicationwith the oil passages 80A and 80B through a pair of check valves (notshown). As will be appreciated by those skilled in the art, whenoperating oil leaks from the closed circuit defined by the transmission22, the charge pump 81 serves to draw lubricating oil in the housing 40,in through an oil filter 86, and communicate the oil to the oil passages80A and 80B in response to the drop in oil pressure in such passages. Itwill also be noted that the lower half housing 40L is provided with anopening 87 releasably covered by a lid 88 to facilitate maintenance ofthe oil fitter 86.

As illustrated in FIGS. 5 and 9, the motor shaft 74 is disposed inparallel to the axle 20L, which simplifies the transmission of driveforce from the motor shaft 74 to the axle 20L. In this regard, in orderto communicate the rotation of the motor shaft 74 to the axle 20L, acounter shaft 89 is provided between the axle 20L and the motor shaft 74which extends parallel to the axle and motor shaft. A gear 90 isprovided on motor shaft 74 which engages with a larger diameter gear 91mounted on the counter shaft 89. A smaller diameter gear 92 on thecounter shaft 89, in turn, engages with a final gear 94 mounted on theaxle 20L. As illustrated in FIG. 9, the counter shaft 89 is preferablypositioned in a first plane P1 which corresponds to the plane of thejoint surface of the housing 40. This allows the axial ends of thecounter shaft 89 to be supported by a pair of bearings interposedbetween the upper and lower half housings 40U and 40L (See FIG. 5). Itwill be understood that the axle 20L can also be disposed in the sameplane P1 such that the bearing 44 which rotatably supports the axle 20Lcan be mounted between the upper and lower half housings 40U and 40L.However, as noted above, disposing the axle 20L on the plane P1 wouldrequire expansion of the lower half housing 40L to accommodate the lowerposition of the final gear 94, thereby undesirably increasing the heightof the housing 40 and decreasing ground clearance. Accordingly, in theillustrated embodiment, the axle 20L is disposed above the plane P1 tominimize the height of the housing 40.

In FIG. 5 a braking mechanism for selectively braking the motor shalt 74is also illustrated. The braking mechanism includes a brake frictionplate 95 fixed on the motor shaft 74 so as to rotate with the shaft 74.Also, a pressure member 96 is provided at one end of a support member98, with the support member 98, in turn, being linked to an operatinglever (not shown) for actuating the brake. When the operating lever isactuated, a cam mechanism 103 causes the pressure member 96 to be placedin press contact with the braking friction plate 95 such that the plate95 is clamped between the pressure member 96 and a stationary brakingplate 99 mounted on the housing 40, thereby enabling the motor shaft 74to be braked. However, the illustrated braking mechanism is merelyillustrative of one suitable braking mechanisms, and other suitablemechanisms can be used if desired.

As shown in FIG. 9, in the preferred embodiment a partition 100 forcovering an upper portion of the final gear 94 is integrally formedupper half housing 40U and an oil flow-through ventilation bore 101 isformed in the partition 100. An opening 102 is formed at a portion ofthe upper wall of upper half housing 40U positioned above the partition100, and covered with a cover member 104. Cover member 104 is providedwith a breather 105 and an oil supply opening 106 releasably covered byan oil supply lid 108. A predetermined amount of oil is charged into thehousing 40 so that the boundary plane of the oil is disposedapproximately as referenced at 109 in FIG. 9. Air mixed in the oil whencharged into the housing is collected in an air reservoir in the covermember 104 through ventilation bore 101. Partition 100 is filled at thelower portion with oil, so that, even when the various gears rotate, theair in the air reservoir is scarcely mixed with oil. When the axledriving unit is operated for a long time, the oil volume expands. Thevolume of air in the air reservoir decreases to accommodate the expandedvolume of oil.

In FIGS. 11 and 12, the right side axle driving unit 18R is shown. Asindicated above, the left and right side axle driving units 18R and 18Lare substantially identical in the preferred embodiment except for thedisposition of the operatively associated axle. Therefore, componentsand features of the unit 18R which are common to the unit 18L discussedabove will be referenced by common reference numerals.

As illustrated, in the right side axle driving unit 18R, the axle 20Rprojects from the right side of the housing, and drive wheel 12R mountsat the distal end of the right axle 20R. In order to rotatably supportthe axle 20R in the housing 40, the axle driving unit 18R is providedwith a third bearing support 110 including a hollow tube portion 113defining a bearing seat for receiving the first roller bearing 44. Thefirst roller bearing 44 rotatably supports the axle 20R proximate thepoint at which the axle projects from the housing 40. In the illustratedembodiment, the third bearing support 110 is provided in the upper halfhousing 40U, but it is contemplated that the roller bearing support 110can be cooperatively defined by the upper and lower half housings 40Uand 40L where the joint surface between the upper and lower halfhousings is alternatively disposed in a common plane with the rotationalaxis of the axle 20R, or can be provided in the lower half housing 40Lwhere the joint surface is disposed in a plane above the rotational axisof the axle 20R A fourth bearing support 111 is also provided whichdefines a bearing seat for receiving the second roller bearing 46. Asillustrated, the second roller bearing 46 supports the proximal end ofthe axle 20R. In the preferred embodiment, the fourth bearing support111 comprises a first component 111A provided oil the upper half housing40U, and a second component 111B provided on the lower half lousing 40Lsuch that the components 111A and 111B cooperatively define the bearingseat for receiving the second roller bearing 46 (See FIG. 12).

As FIGS. 5, 8, 11 and 12 illustrate, in the preferred embodiment of thepresent invention the housing 40 is constructed so as to integrallyprovide the first and second bearing supports 42 and 45 necessary forthe mounting of the left axle 20L and the third and fourth bearingsupports 110 and 111 necessary for mounting the right axle 20R.Depending upon whether the housing 40 is to be used for a left side axledriving unit 18L or a right side axle driving unit 18R, eitherpartitioning wall portion 112L or 112R is removed to accommodate theaxle 20L or 20R. Alternatively, the housing 40 can be manufacturedwithout the partitioning wall portions 112L and 112R, and a separateseal member can be used to seal the unused opening in the housing 40.

In light of the above, it will be appreciated that the axle drivingapparatus of the present invention provides an axle driving unit whichcan be used as either the left or right side axle driving unit withoutsubstantial modifications to either the housing 40 or the internalcomponents of the units. This advantageous construction obviates theneed to construct dedicated left and right side housings, therebygreatly decreasing manufacturing costs. Moreover, the advantageousplacement and construction of the center section 48, allows the housing40 to be greatly reduced in height and width when compared toconventional axle driving units. Accordingly, the axle driving apparatuscan be used on small towers or other small vehicles, and allows thevehicles to define lower centers of gravity so as to improveroadability.

In FIGS. 13-17, an alternate embodiment of the axle driving units of thepresent invention is illustrated. This second embodiment is similar inconstruction to the first embodiment described above so that the sameparts are designated with the same reference numerals and thedescription of common features and components is omitted. Accordingly,only two points of different construction will be described. Further, inFIGS. 13-17 only the left axle drive unit 18L is illustrated, but itwill be understood that in the preferred embodiment the right axle driveunit 18R is substantially identical to the drive unit 18L except for thedisposition of the operatively associated axle.

With respect to the first difference in construction, in many smallmower and small vehicle applications it is advantageous for the axledrive units 18L and 18R to be as narrow in width as possible sinceavailable mounting space on the body frame may be limited. Therefore, inthe second embodiment the enlarged region of the housing 40 iselongated, and the configuration of the center section 48 defines analternative configuration which is efficiently accommodated in themodified enlarged region. In this regard, the pump mounting face 51 andmotor mounting surface 54, formed on upper surface 49 and side surface50, respectively, are formed so that motor mounting surface 54 laterallyoverlaps pump mounting surface 51 by a length L2. Thus, the length L2from input shaft 21 to motor shaft 74 is larger in this embodiment (seeFIG. 16) than in the first embodiment (see FIG. 9) and the cylinderblock 59 of the hydraulic pump is disposed further away from the axle20L than in the first embodiment. As a result of this alternativeconstruction, the center section 48 can be contained in a narrowerenlarged region having a width W2. (see FIG. 13) thereby consuming lesslateral space within the body frame 11.

It will also be noted that the housing 40 of this second embodiment ispreferably provided with a further mounting boss 41C at the utmost endof the enlarged region of the lousing. Mounting boss 41C is connected toa further mounting member 19F provided on the body flame 11 (E.g. seeFIGS. 27 and 29). Given the increased length L1 of the housing of thesecond embodiment, this further mounting boss 41C facilitates the stablemounting of the axle driving unit on the body frame 11.

A second difference is with respect to the motor shaft 74. As in thefirst embodiment, brake friction plate 95 is disposed on one end of themotor shaft 74 that extends outwardly from the housing. The differencein this embodiment is that the other end of motor shaft 74 is providedwith a spline, aid it extends into a through-open bore provided at thecenter of motor mounting surface 54. A bushing 117 is interposed betweenthe joint surfaces of the housing to support a rotary shaft 114 (seeFIG. 13). The spline end of motor shaft 74 is spline-engaged with oneend of the rotary shaft 114 so that the driving force of motor shaft 74is taken out of the housing through rotary shaft 114.

In the preferred embodiment, the outer end of rotary shaft 114 is anindented spline. The braking friction plate 95 can be mounted on thisend of the rotary shaft 114, or the rotary shaft 114 can be used as apower take-out shaft. If such construction is not required, rotary shaft114 can be removed and the bore formed at the joint surfaces of thehousing can be closed by a seal cap.

A third embodiment of the axle driving units of the present invention isillustrated in FIGS. 18-20. It will be noted that the construction ofthis third embodiment is similar to that of the second embodimentdescribed above. However, in the third embodiment, the center section 48is not connected to upper half housing 40U by bolts, but inserted inpart between upper half housing 40U and lower half housing 40L.Therefore, center section 48 is positioned in the enlarged region in afree-standing state. In this regard, housing mounting faces 48 projectfrom the left and right side surfaces of center section 48. Further, theupper surface 49 of the center section 48 and the lower surface 53opposite thereto form housing mounting faces. Since the center section48 is free-standing, bolts are not required such that assembly issimplified and manufacturing cost is lowered.

In order for center section 48 of the third embodiment to befree-standing, input shaft 21 and motor shaft 74 are completelysupported by the housing 40. Upper end of input shaft 21 is supported bya bearing 115 attached to the upper half housing 40U, and the lower endof the input shaft 21 passes through the bore 61 in center section 48and is supported by a bearing 116 mounted in the lid 88 of the lowerhalf housing 40L (see FIG. 19). Motor shaft 74 passes through a bore 61Gin the center section 48 and the opposite ends are supported by bearings118 and 119 (see FIG. 18).

In FIGS. 21-23, a fourth embodiment of the axle driving units of thepresent invention is illustrated. In this embodiment a center section 48of substantially L-like shape in sectional side view is disposed in anelongated enlarged region extending across upper half housing 40U andlower half housing 40L, and is fixed to upper half housing 40U. The pumpmounting surface 51 is formed on a substantially horizontal uppersurface 49, and the motor mounting surface 54 is formed of asubstantially vertical end surface 120 of center section 48. Pumpmounting surface 51 is positioned apart from axle 20R, and motormounting surface 54 is positioned near the axle 20L. The input shaft 21extends substantially vertically and substantially perpendicular to theaxle 20R, and motor shaft 74 extends substantially horizontally andsubstantially perpendicular to axle 20R. It will also be recognized bythose skilled in the art that in this fourth embodiment, the movableswash plate 62 is a cradle-type rather that the trunnion-type swashplate of the above-described embodiments. However, it will be understoodthat cradle-type and trunnion-type swash plates can be interchangeablyused in any of the embodiments discussed herein.

In the fourth embodiment, an oil filter 86 is interposed between thelower surface of center section 48, opposite to the pump mountingsurface 51, and the inner surface of the bottom wall of lower halfhousing 40L. Oil in the housing 40 is filtered by the oil filter 86 andguided to a supply port (not shown) open at the lower surface of centersection 48.

Preferably, the axis of the motor shaft 74 of the fourth embodiment ispositioned in the same plane as the joint surface of the housing suchthat the motor shaft 74 is rotatably supported by bearings interposedbetween the upper half housing 40U and the lower half housing 40L.Further, unlike earlier described embodiments, the axle 20R is disposedin the lower half housing 40L. Motor shaft 74 is substantiallyrectangular to the axle 20R, and passes above the axle 20R. Tile utmostend of the motor shaft 74 projects from the housing, and a brakefriction plate 95 is mounted thereon.

As best illustrated in FIG, 22, the counter shaft 89 extends parallel tothe axle 20R and is substantially perpendicular to the motor shalt 74.Preferably the counter shaft 89 is positioned in the same plane as thejoint surface of the housing such that it can be rotatably supported bybearings sandwiched between the upper half housing 40U and the lowerhalf housing 40L. Since the motor shaft 74 and the counter shaft 89 aresubstantially perpendicular to each other, the gear 90 mounted on themotor shaft 74 and the gear 91 of the counter shaft 89 comprise bevelgears. Accordingly, driving force is transmitted from the motor shaft 74to the counter shaft 89 by bevel gears 90 and 91, and driving force istransmitted from the counter shaft 89 to the axle 20R through gears 92and 94.

A fifth embodiment of the axle driving units of the present invention isillustrated in FIGS. 24-28. In this embodiment, the center section 48 isdisposed in the elongated enlarged region of the housing in asubstantially horizontal orientation. Both the pump mounting surface 51and the motor mounting surface 54 are formed on the upper surface 49 ofthe center section 48 with the motor mounting surface 54 being disposednearest to the axle 20L. The input shaft 21 and motor shaft 74 extend inparallel to each other, and are substantially vertically disposed and atsubstantially right angles to tire axle 20L. It will be recognized thatin embodiments where the motor shaft 74 is horizontally oriented, thewidth of the housing is dictated in large part by the need toaccommodate the length of the motor shaft 74. Thus, by reorienting themotor shaft 74 froth a horizontal position to a vertical position thehousing 40 can be made narrower.

It will be noted that the input shaft 21 is rotatably mounted inessentially the same manner as in the first embodiment. However, themovable swash plate 62 of the fifth embodiment is of a cradle-type, andis manually controllable along the concave circular-arc surface of theinner wall of the upper half housing 40U by using a conventionaloperating mechanism.

With respect to the motor shaft 74 of the fifth embodiment, the upperend of the shaft 74 extends through the fixed swash plate 72 of thehydraulic motor 55, with the fixed swash plate 72 being fixedly fittedinto a concave formed at the inner wall of the upper half housing 40U.The upper end of the motor shaft 74 is rotatably supported by thebearing 75, and projects through the upper half housing 40U. Theprojecting end of the motor shaft 74 carries the braking friction plate95, which rides on a spring member 97. Thus, the braking mechanism ismounted on the top of the housing 40 rather than the side, therebyallowing the axle driving unit to be reduced in width. Further, it willbe noted that the braking friction plate 95 is positioned in theproximity of the cooling fan 63, and ventilation from the cooling fan 63serves to blow away the dust collected on the braking friction plate 95.

The lower end of the shaft 74 projects through a bore 121 provided inthe center section 48 and the motor shaft is rotatably supported in thebore 121 by a bushing 122. In this regard, in the preferred embodimentthe center section is disposed at substantially mid-level along thevertical dimension of the enlarged region of the housing, and thecounter shaft 89, which is substantially parallel to the axle 20L, isdisposed below the center section 48. Tile lower end of the motor shaft74 which projects through the center section 48 carries the gear 90which imparts driving force to the counter shaft 89, with such gear 90defining a bevel gear in this embodiment.

In the fifth embodiment illustrated in FIGS. 24-28, one end of thecounter shaft 89 is rotatably supported by a bearing 124 which issandwiched between the upper and lower half housings 40U and 40L,respectively. The other end of the counter shaft 89 is cooperativelysupported by a projection 123 provided on the lower half housing 40L anda leg member 125 which extends downwardly From the bottom surface of thecenter section 48. More specifically, the projection 123 of the lowerhalf housing 40L defines a semicircular recess 126, and the lowersurface of the leg member 125 defines a further semicircular recess 128,such that the recesses 126 and 128 cooperatively define a receptor forreceiving a bushing 129 which, in turn, rotatably supports the end ofthe counter shaft 89. In the preferred illustrated embodiment, thecenter section 48 and leg member 125 define separate components with asplit pin 130 being provide to maintain the desired relative dispositionof the center section 48 and leg member 125. However, it will berecognized that the leg member 125 can be integrally formed with thecenter section 48.

As illustrated in FIG. 24, the fifth embodiment is provided with amechanism for removing iron powder and metal fragments from the oilwithin the housing 40. In the illustrated embodiment, this mechanismincludes a magnet 131 which is disposed between two partitions 132 and134 provided on the inside wall of the lower half housing 40L. A metalplate member 135 is secured to the partition 132 so as to engage andsecure the magnet 131 in position, the plate member 135 providing asubstantial magnet bonding surface for accumulating iron power and othermetallic particulates.

Whereas the axle driving units 18L and 18R define separate housings 40,and can be separately mounted on the body frame 11, it is advantageousfor the axle driving units 18L and 18R to be secured together to insurethe stable mounting of the axle driving apparatus as a whole, and toinsure the proper alignment of the axles 20L and 20R. Accordingly, asillustrated in FIGS. 27 and 28, the fifth embodiment of the presentinvention is provided with a coupling mechanism referenced generally at136 for securing the housings of the axle driving units 18L and 18Rtogether.

In the preferred embodiment, the coupling mechanism 136 includes a dowelmember 138, the opposite ends of which are closely received in theunused third bearing support 110 of the axle driving unit 18L and theunused first bearing support 42 of the axle driving unit 18R. It will berecognized that this dowel member 138, which in the preferredillustrated embodiment defines a length of pipe, serves to maintain thepositions of the units 18L and 18R such that the axles 20L and 20R arealigned on a common rotational axis. The coupling mechanism 136 alsoincludes a pair of C-shaped coupling brackets 139A and 139B which engageand extend between the mounting bosses 41A and 41B on either side of thebearing supports 110 and 42. Holes are provided in the upper flange ofthe coupling brackets 139A and 139B which register with the mountingbores provided in the mounting bosses 41A and 41B, and which registerwith operatively associated holes provided in the lower flange of thecoupling brackets 139A and 139B. Accordingly, to secure the couplingbrackets in place, bolts 140 are inserted through the holes in the upperflange of the coupling brackets 139A and 13913, through the mountingbores of the mounting bosses and holes of the lower flange of thecoupling bracket, and secured in place.

It will be recognized that the coupling mechanism 136 can be used withany of the illustrated embodiments of the present invention. Further,the illustrated coupling mechanism 136 is merely illustrative of onesuitable mechanism for securing the units 18L and 18R together and it iscontemplated that other mechanism can be interchangeably used.

In FIGS. 29-31, a sixth embodiment of the axle driving units of thepresent invention is illustrated. In this regard, the axle driving units18L and 18R of the sixth embodiment are similar in construction to theunits 18L and 18R of the fifth embodiment. However, in the sixthembodiment no leg member 125 is provided, and, instead, the upper halfhousing 40U and the lower half lousing 40L cooperatively define areceptor 141 in which is mounted a bushing 142 which rotatably supportsthe end of the counter shaft 89.

In light of the above, it will be recognized that the present inventionprovides an axle driving apparatus having great advantages over theprior art. Tile apparatus can be mounted on a relatively small bodyframe, and includes an axle driving unit which call alter natively beused as either a left side or a right side axle driving unit by simplychanging the disposition of the operatively associated axle. Moreover,the apparatus is drivingly connected to the prime mover of a vehicle bya single driving belt, and allows the vehicle on which it is mounted todefine a low center of gravity to improve roadability However, while apreferred embodiment has been shown and described, it will be understoodthat there is no intent to limit the invention to such disclosure, butrather it is intended to cover all modifications and alternateconstructions falling within the spirit and scope of the invention asdefined in the appended claims.

1-29. (canceled)
 30. An axle driving apparatus for a vehicle,comprising: a single axle; a hydraulic pump having a vertical pumpshaft, a cylinder block engaged with the pump shaft containing areciprocally movable piston therein, and a movable swash plate forreceiving thrust from a head of the piston; a hydraulic motor driven bypressurized oil from the hydraulic pump, the motor including a motorshaft drivingly connected to the single axle; and a housing containingthe hydraulic pump, the hydraulic motor, and the single axle, thehousing having a first housing member and a second housing memberseparably joined along a vertical plane perpendicular to a rotary axisof the single axle; wherein a rotary axis of the pump shaft issubstantially parallel to the vertical plane; wherein the hydraulic pumpis entirely disposed in the first housing member and the pump shaftextends outwardly from an upper surface of the first housing member;wherein the single axle defines a longitudinal axis, includes a proximalend portion rotatably mounted in the housing, and includes a distal endportion extending outwardly from a first side of the housing; whereinthe movable swash plate includes a pair of trunnion shafts providedcoaxially at respective opposite sides of the movable swash plate, arotary axis of the trunnion shafts is substantially perpendicular to thevertical plane, each of the trunnion shafts is rotatably supported byone of the first and the second housing members, the movable swash plateis slantingly rotatably supported in the housing, and one of thetrunnion shafts extends outwardly from the housing to be fixed to an armlinked with a speed changing member equipped on the vehicle.
 31. An axledriving apparatus for a vehicle according to claim 30, wherein thehousing defines a length greater than a width thereof, the housingextending rectangularly and horizontally with respect to the rotary axisof the single axle.
 32. An axle driving apparatus for a vehicleaccording to claim 31, wherein a distance from the hydraulic pump to thesingle axle is greater than a distance between the hydraulic motor andthe single axle.
 33. An axle driving apparatus for a vehicle accordingto claim 30, further comprising a center section having a horizontalpump mounting surface disposed relatively lower than the rotary axis ofthe single axle.
 34. An axle driving apparatus for a vehicle accordingto claim 30, wherein the cylinder block has a first end and a secondend, and wherein the rotary axis of the pair of the trunnion shafts islocated between a first horizontal plane located at the first end of thecylinder block and a second horizontal plane located at the second endof the cylinder block.
 35. An axle driving apparatus for a vehicleaccording to claim 34, wherein the movable swash plate includes acontact surface in contact with the head of the piston and anarch-shaped portion for holding the contact surface, wherein thetrunnion shafts are fixed to the side surfaces of the arch-shapedportion, and wherein the contact surface is radially distanced from therotary axis of the trunnion shafts.
 36. An axle driving apparatus for avehicle according to claim 30, wherein the first housing member and thesecond housing member each have a bore with a bearing member disposedtherein, and one of the pair of trunnion shafts is mounted in each bore.37. An axle driving apparatus for a vehicle according to claim 30,wherein the movable swash plate is mounted between the first and secondhousing members to thereby prevent axial movement of the swash plate.38. An axle driving apparatus for a vehicle according to claim 30,wherein the trunnion shaft which extends outwardly from the housingmember is rotatably supported by the second housing member, and extendsoutwardly from the second housing member.
 39. An axle driving apparatusfor a vehicle, comprising: a single axle; a hydraulic pump having avertical pump shaft, a cylinder block engaged with the pump shaftcontaining a reciprocally movable piston therein, and a movable swashplate for receiving thrust from a head of the piston; a hydraulic motordriven by pressurized oil from the hydraulic pump, the motor including amotor shaft drivingly connected to the single axle; and a housingcontaining the hydraulic pump, the hydraulic motor, and the single axle,the housing having a first housing member and a second housing memberseparably joined along a vertical plane perpendicular to a rotary axisof the single axle; wherein a rotary axis of the pump shaft issubstantially parallel to the vertical plane; wherein the hydraulic pumpis entirely disposed in the first housing member and the pump shaftextends outwardly from an upper surface of the first housing member;wherein the single axle defines a longitudinal axis, includes a proximalend portion rotatably mounted in the housing, and includes a distal endportion extending outwardly from a first side of the housing; whereinthe movable swash plate includes a pair of trunnion shafts providedcoaxially at respective opposite sides of the movable swash plate, arotary axis of the trunnion shafts is substantially perpendicular to thevertical plane, each of the trunnion shafts is rotatably supported byone of the first and the second housing members, the movable swash plateis slantingly rotatably supported in the housing, and one of thetrunnion shafts extends outwardly from the housing to be fixed to an armlinked with a speed changing member equipped on the vehicle; wherein themotor shaft is parallel to the trunnion shafts and the single axle;wherein the rotary axis of the single axle is disposed relatively lowerthan the movable swash plate and relatively higher than a rotary axis ofthe motor shaft.
 40. An axle driving apparatus for a vehicle accordingto claim 39, wherein the housing defines a length greater than a widththereof, the housing extending rectangularly and horizontally withrespect to the rotary axis of the single axle.
 41. An axle drivingapparatus for a vehicle according to claim 40, wherein a distance fromthe hydraulic pump to the single axle is greater than a distance betweenthe hydraulic motor and the single axle.
 42. An axle driving apparatusfor a vehicle according to claim 39, further comprising a center sectionhaving a horizontal pump mounting surface disposed relatively lower thanthe rotary axis of the single axle.
 43. An axle driving apparatus for avehicle according to claim 39, wherein the cylinder block has a firstend and a second end, and wherein the rotary axis of the pair of thetrunnion shafts is located between a first horizontal plane located atthe first end of the cylinder block and a second horizontal planelocated at the second end of the cylinder block.
 44. An axle drivingapparatus for a vehicle according to claim 43, wherein the movable swashplate includes a contact surface in contact with the head of the pistonand an arch-shaped portion for holding the contact surface, wherein thetrunnion shafts are fixed to the side surfaces of the arch-shapedportion, and wherein the contact surface is radially distanced from therotary axis of the trunnion shafts.
 45. An axle driving apparatus for avehicle according to claim 39, wherein the first housing member and thesecond housing member each have a bore with a bearing member disposedtherein, and one of the pair of trunnion shafts is mounted in each bore.46. An axle driving apparatus for a vehicle according to claim 39,wherein the movable swash plate is mounted between the first and secondhousing members to thereby prevent axial movement of the swash plate.47. An axle driving apparatus for a vehicle according to claim 39,wherein the trunnion shaft extending outwardly from the housing member,is rotatably supported by the second housing member, and extendsoutwardly from the second housing member.
 48. An axle driving apparatusfor a vehicle, comprising: a single axle; a hydraulic pump having avertical pump shaft, a cylinder block engaged with the pump shaftcontaining a reciprocally movable piston therein, and a movable swashplate for receiving thrust from a head of the piston; a hydraulic motordriven by pressurized oil from the hydraulic pump, the motor including amotor shaft drivingly connected to the single axle; a center sectionhaving a motor mounting surface; and a housing containing the hydraulicpump, the hydraulic motor, and the single axle, the housing having afirst housing member and a second housing member separably joined alonga vertical plane perpendicular to a rotary axis of the single axle;wherein a rotary axis of the pump shaft is substantially parallel to thevertical plane; wherein the hydraulic pump is entirely disposed in thefirst housing member and the pump shaft extends outwardly from an uppersurface of the first housing member; wherein the single axle defines alongitudinal axis, includes a proximal end portion rotatably mounted inthe housing, and includes a distal end portion extending outwardly froma first side of the housing; wherein the movable swash plate includes apair of trunnion shafts provided coaxially at respective opposite sidesof the movable swash plate, a rotary axis of the trunnion shafts issubstantially perpendicular to the vertical plane, each of the trunnionshafts is rotatably supported by one of the first and the second housingmembers, the movable swash plate is slantingly rotatably supported inthe housing, and one of the trunnion shafts extends outwardly from thehousing to be fixed to an arm linked with a speed changing memberequipped on the vehicle; wherein the motor shaft is parallel to thetrunnion shafts; wherein a plane located at the motor mounting surfaceis disposed parallel to the vertical plane and faces the same directionas the trunnion shaft which is opposite to the trunnion shaft extendingoutwardly from the housing
 49. An axle driving apparatus for a vehicleaccording to claim 48, wherein the housing defines a length greater thana width thereof, the housing extending rectangularly and horizontallywith respect to the rotary axis of the single axle.
 50. An axle drivingapparatus for a vehicle according to claim 49, wherein a distance fromthe hydraulic pump to the single axle is greater than a distance betweenthe hydraulic motor and the single axle.
 51. An axle driving apparatusfor a vehicle according to claim 48, wherein the pump mounting surfaceis disposed relatively lower than the rotary axis of the single axle.52. An axle driving apparatus for a vehicle according to claim 48,wherein the cylinder block has a first end and a second end, and whereinthe rotary axis of the pair of the trunnion shafts is located between afirst horizontal plane located at the first end of the cylinder blockand a second horizontal plane located at the second end of the cylinderblock.
 53. An axle driving apparatus for a vehicle according to claim48, wherein the movable swash plate includes a contact surface incontact with the head of the piston and an arch-shaped portion forholding the contact surface, wherein the trunnion shafts are fixed tothe side surfaces of the arch-shaped portion, and wherein the contactsurface is radially distanced from the rotary axis of the trunnionshafts.
 54. An axle driving apparatus for a vehicle according to claim48, wherein the first housing member and the second housing member eachhave a bore with a bearing member disposed therein, and one of the pairof trunnion shafts is mounted in each bore.
 55. An axle drivingapparatus for a vehicle according to claim 48, wherein the movable swashplate is mounted between the first and second housing members to therebyprevent axial movement of the swash plate.
 56. A pair of axle drivingapparatuses for being mounted on the body frame of a vehicle and forindependently rotating first and second wheel members, each of the axledriving apparatus comprising: a housing; a single axle defining alongitudinal axis and having a proximal end portion rotatably mounted inthe housing and a distal end portion extending outwardly from a firstside of the housing; a hydrostatic transmission disposed within thehousing for driving the single axle, the hydrostatic transmissioncomprising a hydraulic pump having a movable swash plate, a hydraulicmotor, and a center section having a pump mounting surface and a motormounting surface for mounting the hydraulic pump and the hydraulic motorat right angles to each other; and a pair of shafts projecting from bothside surfaces of the movable swash plate positioned on an axis ofslanting movement of the movable swash plate, wherein each of the pairof shafts is parallel to the motor shaft, rotatably supported by thehousing, and one of the shafts extends outwardly from the housing to befixed to an arm linked with a speed changing member equipped on thevehicle.
 57. A pair of axle driving apparatuses for a vehicle accordingto claim 56, wherein the housing defines a length greater than a widththereof, the housing extending rectangularly and horizontally withrespect to the longitudinal axis of the single axle.
 58. A pair of axledriving apparatuses for a vehicle according to claim 57, wherein adistance from the hydraulic pump to the single axle is greater than adistance between the hydraulic motor and the single axle.
 59. A pair ofaxle driving apparatuses for a vehicle according to claim 56, whereinthe pump mounting surface is disposed relatively lower than thelongitudinal axis of the single axle.
 60. A pair of axle drivingapparatuses for a vehicle according to claim 56, wherein the motormounting surface faces the same direction as the shaft opposite theshaft extending outwardly from the housing.
 61. A pair of axle drivingapparatuses for a vehicle according to claim 56, wherein thelongitudinal axis of the single axle is disposed relatively lower than atop surface of the movable swash plate and relatively higher than arotary axis of the hydraulic motor.